After six months of a pandemic, researchers are still looking for an answer to a key question about the virus: how deadly it is?
Analyzing the first data of the first outbreaks on cruise ships, and then the performance of thousands of patients from the foci of the epidemic, scientists have already made dozens of calculations of the mortality from covid-19.
Judging by the proportion of deaths of the total number infected, including unregistered cases, covid-19 kills from 0.3% to 1.5% of cases. Most of the studies gives a mortality in the range of 0.5% to 1.0%, meaning that out of every thousand cases on average die 5 to 10 people.
According to these estimates it appears that the new coronavirus deadlier than seasonal flu, but not as dangerous as Ebola and other infectious diseases that have appeared in recent years. The coronavirus is killing more people — partly because more contagious.
“One mortality rate among the infected is not limited. We still have to see how this disease is contagious, and covid extremely contagious,” said Eric Toner (Eric Toner), a doctor of emergency medicine and senior researcher, Center for health security at the Johns Hopkins University, which examines the readiness of the health care system to epidemics and infectious diseases. “It is the combination of mortality and infectivity makes this disease so dangerous.”
Health authorities and researchers are working to measure the mortality rate from coronavirus to better understand the risks involved, estimate how many people might die, and take the necessary epidemiological measures.
However, to identify this indicator was difficult because a significant portion of cases is oligosymptomatic or even detected with tests. The mortality rate also varies depending on such factors as the patient’s age and efficiency of the health system in the country.
“It is very difficult to measure, but dense research catch in the noise of a clear signal,” says researcher at the London school of hygiene and tropical medicine Timothy Russell (Timothy Russell).
According to Dr. Russell and his colleagues, whose study is based on data from China and the outbreak on Board the cruise liner “diamond Princess” (Diamon Princess) was released in February, the mortality rate is about 0.6%.
According to the Johns Hopkins University, just a strain of the virus SARS-CoV-2 around the world infected more than 14.7 million people and killed more than 609 thousand, and more than a quarter of them in the United States. This means that the mortality rate among patients was approximately 4.2%.
The researchers say that the mortality rate among patients with identified infection is higher than among the population generally, because many of the lung and asymptomatic cases covid-19 is not considered.
Center for control and prevention of diseases of the USA has estimated that for every identified case covid-19 in early may, accounted for approximately 10 undetected. In an article published in the journal JAMA Internal Medicine on Tuesday, the Agency reported that from March to may, the total number of infected exceeded the number of cases in the 6 to 24 times, depending on the state.
“To understand how many people are infected, it is difficult,” says Lucy Okell (Lucy Okell) from Imperial College in London. According to the calculations of her colleagues, in March the mortality rate in China was 0.66%.
In order to properly evaluate the mortality rate, some researchers take the cases and number of deaths, and then roughly estimate the proportion of missed or asymptomatic cases. In addition, their calculations can slip in undetected death from covid-19, and it is also necessary to take into account.
Other researchers build assessments based on tests for antibodies when a blood test revealed signs of infection.
But this method has its drawbacks, as scientists still do not fully understand how it works the immune response to the virus. In addition, we have to somehow compensate for the risk of false results, or the gap between infection and death.
But regardless of the approach, for a precise fit to their estimates, the researchers used sophisticated mathematical models and statistical methods.
In one not-yet-peer-reviewed report, published in July on the server preprints medRxiv, the analysis of 26 different estimates of mortality in different parts of the globe showed the aggregate level of 0.68% in the range from 0.53% to 0.82%.
“I believe that someday we will get a common rating, which is absolute truth, is wrong. We can get an idea about certain trends, but it must remember that it can change,” says epidemiologist and economist Lea Merone (Lea Merone) from James cook University in Australia, co-author of the article. “It all depends on the situation,” she concludes.
Currently, the Center for control and prevention of diseases of the United States took this prediction as a basis for optimal estimation of mortality rates and further planning of the pandemic and its scenarios. As of 10 July, the rating Agency is 0.65 percent higher than the previous one.
Studies show that the mortality rate among patients varies, and considerably, depending on such factors as age, gender and associated diseases in anamnesis.
Researchers from USA and Switzerland have calculated mortality rates for different age groups based on data from the Swiss city of Geneva found that among people older than 65 years, mortality from infections is 5.6%, which is 40 times higher than for fifty years.
The mortality rate varies depending on the quality of treatment and availability of medical care. Optimal future treatments will help to reduce the incidence of disease, but the situation when the hospital system is overloaded with potential for increased morbidity, says an epidemiologist from the University of Wollongong Gideon of Meyerowitz Katz (Gideon Meyerowitz-Katz), co-author of the July article in MedRxiv.
The mortality rate of 0.6%, approximately six times the forecast for seasonal flu according to the Center for control and prevention of diseases of the USA it is 0.1%. The researchers note that the forecasts are calculated differently, and evaluation for influenza does not take into account asymptomatic cases.
Diseases like severe acute respiratory syndrome (SARS), middle East respiratory syndrome (BRS) or Ebola is much deadlier — their mortality ranges from 10% to 50%.
And yet this disease has claimed far fewer lives than the new coronavirus, or even seasonal flu, because they are not contagious and are less common.
From the SARS BRS умерло774 and 858 people, respectively. Ebola has claimed more than 300 lives 11.
In addition, many doctors fear that covid-19 can lead to long-term complications in some patients — especially those who patient spent several weeks in the hospital.
“There is a widespread belief that ill, you either die, or everything is getting better quickly. That’s not true, says Dr. Toner. — People who are seriously ill, faces not only death, but also the consequences for health”.